Hi, I’ve housed some together with no problems, but they were the same size. Most problems are caused by both snakes going after the same mouse. I never keep two snakes together anymore. There is also the risk of the female being bred too early. But, if you do decide to keep them together, quarantine the new female for at least three months. And believe me, you might find she’s healthy now, but in a month she’s showing signs of a uri. I know this from experience.